There has been considerable interest in hormones which affect the release of hormones from the anterior lobe of the pituitary gland, in particular luteinizing hormone (LH) and follicle-stimulating hormone (FSH). A variety of hypophysiotropic peptides or proteins have been reported to be present in mammalian gonads. Gonadotropin releasing hormone (GnRH), a decapeptide, which is also known as luteinizing hormone release factor (LRF) is a peptide found to stimulate the release of both LH and FSH. Proteins termed "inhibins", which selectively suppress the secretion of FSH but, under most circumstances, do not suppress the release of LH, have been recently isolated and characterized from gonadal fluids of several species, Robertson et al., Biochem. Biophys. Res. Commun. 126, 220-226 (1985); Miyamoto et al., Biochem. Biophys. Res. Commun. 129, 396-503 (1985); Rivier et al., Biochem. Biophys. Res. Commun. 133, 120-127 (1985); Ling et al., P.N.A.S. 82, 7217-7221 (1985). Mason et al., Nature, 318, 659-663 (1985) disclosed the complete amino acid sequences of porcine inhibin .alpha. subunit and two distinct .beta. subunits, .beta..sub.A and .beta..sub.B. Gonadotropin-releasing peptides have also been described in the gonads which have generally been shown to have activity in radioreceptor assays for GnRH but to exhibit different chromatographic and immunologic characteristics from that of GnRH, Igarashi et al. Endocrinology 74: 446-452 (1964); Igarashi et al., In Psychoncuroendocrinology, ed. by Hatotani et al., pp. 178-186 (1973); Lundanes et al., Biochem. Biophys. Res. Commun. 94: 827-836 (1980) and Samson et al., Peptides 1:97-102 (1980).
Described herein are proteins which are found in mammalian follicular fluid and which have action opposite that of inhibin, stimulating the release of FSH from the pituitary but not stimulating the release of LH. Such a peptide is generally referred to herein as "FSH-releasing peptide" (FRP) but is sometimes also referred to as "activin".